#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

char*mmap();
#define rd(v) int v=0;{int _c;while(_c=*rp++-48,_c>=0)v=v*10+_c;}

char wbuf[1<<25];
#define wt(v) {long _z=v;do*--wp=_z%10+48;while(_z/=10);}

#define rep(v,e) for(int v=0;v<e;++v)

int a[200000];
int indirect_sort_buf[200000];
int index[2000000];

#define indirect_sort_aux(sh,ia,ib)      \
{                                        \
	int c[256];                          \
	for(int i=0;i<256;++i){              \
		c[i]=0;                          \
	}                                    \
	for(int i=0;i<n;++i){                \
		++c[a[ia[i]]>>sh&255];           \
	}                                    \
	int t=0;                             \
	for(int i=0;i<256;++i){              \
		int u=c[i];                      \
		c[i]=t;                          \
		t+=u;                            \
	}                                    \
	for(int i=0;i<n;++i){                \
		ib[c[a[ia[i]]>>sh&255]++]=ia[i]; \
	}                                    \
}                                        \

void indirect_sort(int*ia,int n){
	indirect_sort_aux( 0,ia,indirect_sort_buf);
	indirect_sort_aux( 8,indirect_sort_buf,ia);
	indirect_sort_aux(16,ia,indirect_sort_buf);
	indirect_sort_aux(24,indirect_sort_buf,ia);
}

main(){
	char*rp=mmap(0l,1l<<25,1,2,0,0ll);
	rd(n);
	rep(i,n){
		rd(ai);
		a[i]=ai;
		index[i]=i;
	}
	indirect_sort(index,n);

	char*wp=wbuf+sizeof wbuf;
	*--wp='\n';
	*--wp='1';

	int on=0;
	for(int i=0;i<n;i+=2){
		if(on){
			*--wp=' ';
			wt(index[i]+1);
		}
		on^=index[i]==0;
	}
	for(int i=n-2|1;i>0;i-=2){
		if(on){
			*--wp=' ';
			wt(index[i]+1);
		}
		on^=index[i]==0;
	}
	for(int i=0;i<n;i+=2){
		if(on){
			*--wp=' ';
			wt(index[i]+1);
		}
		on^=index[i]==0;
	}
	for(int i=n-2|1;i>0;i-=2){
		if(on){
			*--wp=' ';
			wt(index[i]+1);
		}
		on^=index[i]==0;
	}

	write(1,wp,wbuf+sizeof wbuf-wp);
	_exit(0);
}